The present invention is directed to a system for reducing the harmful exhaust gas emissions of internal combustion engines and, more particularly, to a method and apparatus for containing and reducing the harmful exhaust gas emissions of engines having catalytic converters that are inefficient at low temperatures.
Exhaust gas emissions are the worst during approximately the first 60 seconds of the operation of an engine employing a catalytic converter because the catalytic converter is below its "light-off" temperature and unable to effectively reduce harmful exhaust emissions. Exhaust gas emissions may also be high at the beginning of engine operation because the fuel-air mixture may be fuel-rich during engine starting.
An expandable exhaust container can be used to trap the exhaust emissions during engine starting, however expandable exhaust containers are not expected to attain durability requirements at reasonable cost. A further problem with expandable exhaust containers is that they cannot be packaged easily into available spaces within the automobile. The expandable exhaust container could be made smaller for improved packaging within the automobile, however, that would compromise the ability of the expandable exhaust container to trap the harmful exhaust emissions. Expandable exhaust containers are shown in U.S. Pat. No. 3,645,098 issued to Robert J. Templin et al. (Feb. 29, 1972), and in SAAB Automobile AB press release titled "Saab Exhaust Recirculation Concept: Dramatically reduced cold-start emissions" (March 1996). Durability is a significant problem considering that the state of California has enacted new tailpipe emission regulations including an exhaust emission control system certification requirement of 120,000 miles or 12 years, whichever occurs first (State of California, Air Resources Board, Amendments to California Exhaust, Evaporative and Refueling Emission Standards and Test Procedures for Passenger Cars, Light-duty Trucks and Medium-duty Vehicles "LEV II", enacted Nov. 5, 1998). Durability, and consequently material and manufacturing costs, are expected to continue to be significant problems for expandable exhaust containers considering the temperature and the adverse chemical composition of the exhaust gas.
As an alternative to trapping all of the exhaust gas during engine starting in an expandable exhaust container, U.S. Pat. No. 3,645,098 shows an exhaust canister with trapping agents that trap the harmful constituents of the exhaust gas and that lets the inert non-harmful constituents of the exhaust gas flow out of the canister. A problem with exhaust gas canisters with trapping agents is that they do not effectively trap all of the harmful constituents of the exhaust gas. A further problem with exhaust gas canisters with trapping agents is that of insufficient durability. In particular, the temperature and water content of the exhaust gas can degrade the effectiveness and functional life of low-cost low-temperature trapping agents such as activated charcoal. Flow of exhaust gas through the trapping agent could be terminated before the trapping agent overheats to improve durability, however that would compromise the ability of the trapping agent to trap harmful exhaust emissions.
California enacted a Super Ultra Low Emission Vehicle (SULEV) standard, that has emission certification levels 93% more stringent than the current ULEV standard for oxides of nitrogen (NOx), 82% more stringent for non-methane organic gasses (NMOG), and 75% more stringent for particulate matter (PM). Honda has a prototype emission system capable of attaining the proposed SULEV emission levels, however, system durability to 100,000 miles is a problem and Honda has stated that its technology currently costs about $1000 more than its current production emission systems, which is prohibitively expensive.
Therefore, the objectives of the present invention are to employ an exhaust container having a ridged non-expandable construction to achieve and/or surpass durability requirements, to retain and recirculate to the engine all of the exhaust gas during engine starting to prevent or minimize exhaust of some of the harmful exhaust gas constituents, to have a small size practical for automotive applications and to have a low cost. A further objective is to provide an exhaust container that can easily be form fit into the spaces available within the vehicle.